Identification of nonlinear bolted lap-joint parameters by force-state mapping

Joints and fasteners often have a significant effect on the dynamical behaviour of assembled mechanical structures and the analytical prediction of structural responses therefore depends upon the accuracy of joint modelling. Detailed constitutive models that fully describe the behaviour of frictional interfaces are often unduly complicated; in which case simpler phenomenological models having parameters identified from vibration tests may be preferable. Unfortunately the direct measurement of forces transmitted between two contacting surfaces and their relative displacements are not possible in practice and it is therefore necessary to rely on measurements remote from joints. In this paper, the parameters of an assumed nonlinear joint model are identified by force-state mapping from time-domain acceleration records in response to single-frequency excitation close to the first natural frequency. The problem of lack of accessibility for measurement at the joint is overcome by casting the governing equation of the system in modal coordinates so that modal parameters are identified to represent the nonlinear behaviour of the joint. A particular result from the experimental programme is the identification of viscous damping coefficients dependent upon displacement amplitude. The significance of this result is that the complex phenomenon of energy dissipation in lap joints can be represented by a simple analytical model capable of producing accurate results.     

Nonlinear model updating of frictional structures through frequency–energy analysis

Nonlinear Dynamics - Recently, some researchers have suggested using frequency–energy representations of nonlinear normal modes (NNMs) for nonlinear model updating of conservative systems....     

Half-metallic properties of the Co2Ti1−xFexGa Heusler alloys and Co2Ti0.5Fe0.5Ga (0 0 1) surface

Electronic and magnetic properties of the bulk Co₂Ti_1−xFe_xGa Heusler alloys and Co₂Ti_0.5Fe_0.5Ga (0 0 1) surfaces are studied within the framework of density functional theory using the augmented plane wave plus local orbital (APW+lo) approach. It will be shown that all alloys have the spin polarization of the ideal 100% value except the Co₂FeGa alloy with spin polarization about 98%. Co₂Ti_0.5Fe_0.5Ga is an example that is stable against the effects destroying the half-metallicity due to the position of the Fermi energy (E_F) in the middle of the minority band gap. The phase diagram obtained by ab-initio atomistic thermodynamics shows that in the higher limit of μ_Ga three surfaces of FeGa, TiGa and TiFeGa are accessible in the Co₂Ti_0.5Fe_0.5Ga alloy but on decreasing μ_Ga, the accessible region gradually moves towards FeGa termination. It is discussed that, at the ideal surfaces, half-metallicity of the alloy is lost, although the TiGa surface keeps high spin polarization (about 95%).     

An experimental and numerical study of packing,compression, and caking behaviour of detergent powders

This paper presents an experimental and numerical study of the packing, compression, and caking behaviour of spray dried detergent(SDD) powders with a two-fold aim: an experimental process of observation and evaluation of the packing, compression and caking behaviour of SDD powders, and a numerical approach based on discrete element modelling(DEM). The mechanical properties, including the stress–strain response and the corresponding porosity change as a function of consolidation stress in a confined cylinder, the stress–strain response during unconfined shearing and the cake strength as a function of consolidation stress, were evaluated and compared for different SDD powders using an extended uniaxial tester(Edinburgh Powder Tester – EPT). The experiments using EPT showed excellent reproducibility in the measurement of packing, compression and caking behaviour and were therefore very useful for describing the handling characteristics of these powdered products including screening new products and different formulations. It was found that the sample with higher moisture had lower bulk porosity but higher compressibility and cake strength. The porosity, compressibility and cake strength were found to vary across different size fractions of the same sample. The larger sieve-cut samples had higher initial bulk porosity, compressibility and cake strength. It is revealed that moisture plays a significant role in packing, compression, and shearing behaviour of the powder. Three-dimensional DEM modelling using a recently developed elasto-plastic adhesive-frictional contact model showed that the contact model is able to capture the detergent behaviour reasonably well and can be used to model complex processes involving these powders.     

Identification of Iwan distribution density function in frictional contacts

Mechanical contacts affect structural responses, causing localized nonlinear variations in the stiffness and damping. The physical behaviors of contact interfaces are quite complicated and almost impossible to model at the micro-scale. In order to establish a meaningful understanding of the friction effects and to predict the contact behavior, a robust parametric friction model is usually employed. This paper employs an Iwan-type model to predict the nonlinear effects of a frictional contact interface. The Iwan model is characterized by its distribution density function which is commonly identified by double differentiation of the experimentally obtained joint interface restoring force. Direct measurement of restoring forces at the contact interface is impractical and estimating it using an inverse approach introduces considerable uncertainties in identification of the density function. This paper develops a more reliable procedure in identification of the Iwan model by relating the density function to the joint interface dissipated energy. The energy dissipated in a contact interface is easily obtained from measurement and it is shown that the dissipation is uniquely defined using the density function and the vibration amplitude. In an experimental case study Iwan distribution density function in a frictional contact is obtained using measured dissipations at different vibration levels.     

Vibrational analysis of electrostatically actuated microstructures considering nonlinear effects

The vibrational behavior of electrostatically actuated microstructures subjected to nonlinear squeeze film damping and in-plane forces is investigated. First-Order Shear Deformation Theory is used to model dynamical system by means of finite element method, while finite difference method is applied to solve the nonlinear Reynolds equation of squeeze film damping simultaneously. Vibrational analysis of microplates is performed by solving eigenvalue problem, after validating the model by pull-in phenomenon and transient behavior. In addition, considering nonlinear squeeze film damping and step-input actuations, response frequencies of microplates are calculated. Effect of ambient pressure and in-plane forces on dynamic pull-in phenomenon is also studied. Results for simplified models are verified and are in good agreement with the published literature. This investigation can reveal nonlinear vibrational behavior of microstructures.     

Study of various aliphatic alcohols as sacrificial agents on photoelectrochemical behavior of nickel-platinum-modified Cr-TiO<Subscript>2</Subscript> nanotubes

Cr-TiO₂ nanotubes (Cr-TNTs) have been synthesized via facile one step anodization, followed by co-deposition by nickel-platinum via electroless deposition method. Field-emission scanning electron microscopy (FE-SEM), x-ray diffraction (XRD), and Raman spectroscopy have then been used to characterize the surface morphology and structure of the synthetic samples. The optical properties of the compounds have been investigated by ultraviolet-visible (UV-Vis) diffuse reflectance spectroscopy. Linear sweep voltammetry (LSV) and chronoamperometry were used to study the photoelectrochemical behavior of the obtained samples. The best electrochemical performer sample (t₂₀) was recognized and evaluated in the presence of various aliphatic alcohols, as sacrificial agents, in photoelectrochemical cells (PEC) water splitting. In terms of sacrificial agent used, photocurrent density production was as follows: methanol > ethanol > glycerol > n-propanol > isopropanol > ethylene glycol. Also methanol concentration was optimized. Thus, both co-deposition of Cr-TNTs and addition of scavengers are promising methods to enhance the performance of catalysts for PEC.     

Single-nucleotide polymorphism analysis by allele-specific extension of fluorescently labeled nucleotides in a microfluidic flow-through device

We describe a microfluidic approach for allele-specific extension of fluorescently labeled nucleotides for scoring of single-nucleotide polymorphism (SNP). The method takes advantage of the fact that the reaction kinetics differs between matched and mismatched configurations of allele-specific primers hybridized to DNA template. A microfluidic flow-through device for biochemical reactions on beads was used to take advantage of the reaction kinetics to increase the sequence specificity of the DNA polymerase, discriminating mismatched configurations from matched. The volume of the reaction chamber was 12.5 nL. All three possible variants of an SNP site at codon 72 of the p53 gene were scored using our approach. This work demonstrates the possibility of scoring SNP by allele-specific extension of fluorescently labeled nucleotides in a microfluidic flow-through device. The sensitive detection system and easy microfabrication of the microfluidic device enable further miniaturization and production of an array format of microfluidic devices for high-throughput SNP analysis.     

Molecularly imprinted polymer on a SiO2‐coated graphene oxide surface for the fast and selective dispersive solid‐phase extraction of Carbamazepine from biological samples

A surface carbamazepine‐imprinted polymer was grafted and synthesized on the SiO₂/graphene oxide surface. Firstly SiO₂ was coated on synthesized graphene oxide sheet using the sol–gel technique. Prior to polymerization, the vinyl group was incorporated on to the surface of SiO₂/graphene oxide to direct selective polymerization on the surface. Methacrylic acid, ethylene glycol dimethacrylate and ethanol were used as monomer, cross‐linker and porogen, respectively. Nonimprinted polymer was also prepared for comparison. The properties of the molecularly imprinted polymer were characterized using field‐emission scanning electron microscopy and Fourier‐transform infrared spectroscopy. The surface molecularly imprinted polymer was utilized as an adsorbent of dispersive solid‐phase extraction for separation and preconcentration of carbamazepine. The effects of the different parameters influencing the extraction efficiency, such as sample pH were investigated and optimized. The specificity of the molecular imprinted polymer over the nonimprinted polymer was examined in absence and presence of competitive drugs. The carbamazepine calibration curve showed linearity in the ranges 0.5–500 μg/L. The limits of detection and quantification under the optimized conditions were 0.1 and 0.3 μg/L, respectively. The within‐day and between‐day relative standard deviations (n = 3) were 3.6 and 4.3%, respectively. Furthermore, the relative recoveries for spiked biological samples were above 85%.